Adaptive Critic Design for Energy Minimization of Portable Video Communication Devices

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1 daptve rtc Desg for Eergy Mmzato of Portable Vdeo ommucato Devces Zhao Su Natoal Isttute of erospace North arola & State Uversty N 74 US X he ad Zhha He Departmet of Electrcal ad omputer Egeerg Uversty of Mssour olumba MO bstract Portable vdeo commucato devces operate o batteres wth lmted eergy supply. However vdeo compresso s computatoally tesve ad eergy-demadg. herefore oe of the cetral challegg ssues portable vdeo commucato system desg s to mmze the eergy cosumpto of vdeo ecodg so as to prolog the operatoal lfetme of portable vdeo devces. I ths work we cosder a vdeo ecoder as a olear system wth a umber of ecoder parameters to ts power cosumpto. We explore the approach of adaptve crtc desg to cotrol ad optmze the power cosumpto behavor of a portable vdeo ecodg system. Our expermetal results demostrate that ths approach s very effcetly beg able to acheve the optmum performace accurately ad robustly. Keywords- vdeo compresso eergy mmzato adaptve cotrol optmzato. I. INRODUION ORBE devces are powered by batteres. Vdeo Pecodg schemes are stll computatoally tesve ad eergy-demadg eve after beg fully optmzed wth exstg software ad hardware eergy-mmzato techques [ 4 8]. s a result the operatoal lfetme of curret portable vdeo systems such as hadheld vdeo devces s stll very short mostly the rage of a few hours. hs has become a bottleeck ssue for techologcal progress portable vdeo electrocs. I the age of desktop computg ad wred commucato people worred about bts storage space or trasmsso badwdth. o aalyze model cotrol ad optmze the performace of a sgal processg ad commucato system uder bt rate costrats ratedstorto (R-D theores ad algorthms have bee developed []. Wth recet techologcal advaces crcut desg ad wreless commucato the storage space ad etwork badwdth have expereced dramatc growth beg mproved by hudreds of tmes durg the past decade. urretly may portable commucato applcatos eergy has become a much more scarce ad crtcal resource tha bts [8]. herefore how to corporate the eergy cosumpto to the exstg R-D performace aalyss framework so as to optmze the commucato system performace uder bt ad eergy costrats emerges as a ew research ssue. here are two types of portable vdeo devces: ecoder (e.g. vdeo cell phoes wreless vdeo cameras etc ad player (e.g. Pod vdeo. I ths work we focus o eergy mmzato for portable vdeo ecodg devces. hs s because o portable vdeo devces the fracto of eergy cosumpto by vdeo ecodg (typcally 6-85% s much hgher tha that of vdeo decodg. o reduce the eergy cosumpto of vdeo ecoders a lot of algorthms software ad hardware eergy-mmzato techques cludg lowcomplexty ecoder desg low-power embedded vdeo ecodg adaptve power cotrol ad jot ecoder ad hardware adaptato have bee developed [ 4 8 9]. hese algorthms focus o ecoder complexty (ad power cosumpto reducto through heurstc adaptato or cotrol stead of systematc eergy optmzato. I ths work we propose to develop a systematc approach to cotrol ad optmze the eergy cosumpto behavor of portable vdeo ecodg devces usg adaptve crtc desg [6]. More specfcally we cosder the vdeo ecoder as a olear dyamc system. he purpose of eergy cosumpto cotrol s to fd a sequece of ecodg parameters such that the overall eergy cosumpto s mmzed uder the rate-dstorto costrats. Our expermetal results demostrate that ths olear system cotrol approach s very effectve beg able to acheve the optmum performace. he rest of the paper s orgazed as follows. I Secto II we dscuss eergy-scalable vdeo ecodg system desg. Secto III presets our adaptve crtc system desg. Secto IV presets the expermetal results o eergy cosumpto cotrol ad optmzato real-tme vdeo ecodg. Secto V cocludes the paper. II. OPERION POWER-RE-DISORION NYSIS I ths secto we study the eergy cosumpto behavor of a vdeo ecoder ad troduce the operatoal power-ratedstorto (P-R-D aalyss. he operatoal P-R-D aalyss wll be performed offle ad provde the groud-truth optmum performace whch wll be used for performace evaluato of the proposed algorthm. he cetral task of P-R-D aalyss s to aswer the followg questo []: what s the mmum vdeo dstorto (or equvaletly vdeo qualty that a vdeo ecoder ca /8/$5. 8 IEEE

2 acheve uder bt rate ad power cosumpto costrats? Fgure : optmum ecoder cotrol parameters. Fgure. P-R-D fucto. Our cetral dea s to troduce a set of complexty cotrol parameters to cotrol (scale dow the computatoal complexty of major ecodg operatos of the vdeo ecoder. Wth DVS (Dyamc Voltage Scalg a recetly developed power cotrol techology for mcroprocessors [] ths complexty-scalable vdeo ecoder ca be traslated to a eergy-scalable vdeo ecoder. More specfcally the eergyscalable vdeo ecoder desg has the followg three major steps. I the frst step we group the ecodg operatos to several modules such as moto predcto pre-codg (trasform ad quatzato ad etropy codg ad the troduce a set of cotrol parameters Γ = [... ] to cotrol the power cosumpto of these modules. herefore the ecoder complexty s the a fucto of these cotrol parameters deoted by (.... Wth the DVS desg framework the ecodg power cosumpto deoted by P s a fucto of ecoder complexty therefore also a fucto of Γ = [... ] deoted by P(.... he expresso of ths fucto also depeds o the power cosumpto model of the specfc mcro-processor. I the thrd step ether expermetally or aalytcally we study the R-D behavor of each cotrol parameter ad tegrate these models to a comprehesve parametrc R-D model for the vdeo ecoder deoted by D( R;.... We perform optmum cofgurato of the cotrol parameters to maxmze the vdeo qualty (or mmze the vdeo dstorto uder the power costrat. hs optmzato problem ca be mathematcally formulated as follows: m D = D( R;... {... } s.t. P... P ( ( where P s the avalable power cosumpto for vdeo ecodg. he optmum soluto deoted by D ( R; P descrbes the P-R-D behavor of the vdeo ecoder. o vew the P-R-D model more detal we plot the D-P curves for dfferet bt rates ragg from. bpp (bts per pxel to. bpp Fg.. Fg. shows the D-P curves at dfferet bt rates R s. Fg. shows the optmum complexty cotrol parameters. We ca see that whe the power supply level s low the D(R fucto s almost flat whch meas the vdeo processg ad ecodg effcecy s very low; hece ths case more badwdth does ot mprove the vdeo presetato qualty. he P-R-D model has drect applcatos eergy maagemet resource allocato ad QoS provsog wreless vdeo commucato especally over wreless vdeo sesor etworks. Fgure : P-R-D fucto.

3 III. DPIVE RII DESIGN FOR ENERGY ONRO ND OPIMIZION It should be oted that the operatoal P-R-D aalyss proposed the prevous secto volves very hgh computatoal complexty. It s teded for offle modelg ad aalyss oly ad ot sutable for real-tme eergy cosumpto cotrol ad optmzato. I ths work based o the acto-depedet ad globalzed dual heurstc dyamc programmg (DGDHP method we desged a optmal cotroller for real-tme eergy cosumpto cotrol ad optmzato [6 7]. he adaptato DGDHP s show Fg. 4. It cossts of three major compoets: a model etwork a crtc etwork ad a acto etwork. he puts to the model etwork are system state varable X ( k = [ D( k P( k R] ad ecoder cotrol parameters k ( = [ ( k ( k ( k ]. Here D(k ad P(k are vdeo codg dstorto ad ecodg power cosumpto at tme (or frame k. We assume a rate cotrol algorthm operates sde the ecoder such that the ecodg bt rate R remas relatvely costat throughout the process. I ths work we set k ( = [ ( k ( k ( k ] to be the complexty cotrol parameters Γ = [... ]. he output of the model etwork s the system state at the ext tme stace. he task of the crtc etwork s to lear the cost-to-go performace metrc fucto J(k whle the acto etwork wll determe the ecoder cotrol parameters k ( = [ ( k ( k ( k ] to mmze J(k. I the followg we wll dscuss detaled desg of these three etworks. Fgure 4: block dagram of the proposed DGDHP desg for eergy cosumpto cotrol ad optmzato.. rtc Network Desg Dyamc programmg s a geeral approach for sequetal optmzato applcable uder very broad codtos. Fudametal to ths approach s Bellma Prcple of Optmalty [5]: f a trajectory of actos s optmum o matter how a termedate pot s reached the rest of the trajectory must cocde wth a optmal trajectory as calculated wth the termedate pot as the startg pot. hs prcple s appled by formulatg a "prmary" utlty fucto U(t that represets a cotrol objectve for a partcular cotext oe or more measurable varables. secodary utlty fucto s the formed: K J ( t = U( t+ k ( k= Ufortuately mmzato of J(t s ot computatoally tractable for most real applcatos. Istead the Bellma recurso s ofte used: J ( t = U ( t + J ( t + ( where s a dscout factor for fte horzo problems ( < r < ad U(t s the utlty fucto or local cost. crtc eural etwork show Fg.5 s used to estmate J(t. Here we chose hdde euro thus = wth weghts w = [ w w w w w w w ]( = V = V V V V s the weght of the output euro. I ths eural etwork we have: q = [ D P R ] W S = σ ( q = (4 q + e J = [ S S S] V he crtc NN outputs the scalar J ad two vectors λ X ( k + ad λ ( k +. J s the cost fucto estmated as: hc J( k = Vc( k S ( k where S ( k = σ ( q( k = q = + e 6 q ( k = wj ( k I j= ( k ( I ( k = ( k j Jk ( + λx = [ λx λ ] [ ] ( X λ X = λ D λp λr whrere λx k + = X ( k + λ = [ λ λ λ ] where λ ( k + = ( k + (5 It should be oted that acto depedet forms of D s we have X( k + = λx ( k + l( k = l( k (6 m X ( k + * l( k = λx ( k + + ( λ k l X j( k = X j( k l= X j( k where * J ( k + U( k λ l ( k = + (7 l( k l( k m are the dmeso of the output of the model ad the acto etworks respectvely. he crtc etwork tres to mmze the followg error measure over tme: ( ( ( E = E ( ( k + ER k ER k + E k E k where k k k

4 E = E ( k + E ( k E ( k + E ( k E ( k x x k k k E ( k = Jk ( Jk ( + Uk ( J( k U( k E ( k = ( E ( k R x x j X j( k X j( k X j( k J( k J( k + U( k E ( k = ( E ( k R m l l( k l( k l( k s the dscout factor ( < <. We apply the MS algorthm ad t results a update rule as below: m J( k J( k J( k + U( k J( k J( k J( k + U( k J( k η Δ w = η E ( k η [ ] + η [ ] w X ( k X ( k X ( k X w ( k ( k ( k w j s t = = s s s s t t t t j j j η η are three postve learg rates wth respect to the three tug paths Fg.. Fgure 5: rtc eural etwork. B. cto Network Desg he acto NN has a smlar structure as that of the crtc NN. Fg. 5 also shows the drect adaptato path λ ( k + betwee the acto ad the crtc etworks. he goal of acto s trag s to make λ (t the dervatve of J(t wth respect to the acto to approach zero. o tra the acto etwork we use oly the crtc s J / outputs so as to meet the equato above. hus the error acto s: E = λ ( k + λ( k + (5 he put of acto NN s the state vector X ad the output s the cotrol or acto vector. he weght update rule ca me smply expressed as follow: k ( Δ W = η [ λ( k + ] (6 W where η s a postve learg rate of the acto NN.. Model Neural Network Desg he objectve of model NN s to predct the ext system state X(k+ for gve curret system state X(k ad acto vector (or ecoder cotrol parameters (k. o do ths we also use the eural etwork show Fg. 5. I vdeo ecodg we are able to drectly measure the system state varables. et Y(k+ = [D(k+ P(k+ R(k+] (7 be the measured system state varables amely the ecoded vdeo qualty D(k+ ecodg bt rate R(k+ ad ecodg power P(k+. he the error modelg s gve by E = [ Y ( k + X ( k + ] [ Y ( k + X ( k + ] (8 whch ca be used to tue the weghts of the model eural etwork. IV. ENERGY ONSUMPION ONRO ND OPIMIZION FOR RE-IME VIDEO ENODING I vdeo ecodg there are three computatoally tesve operatos amely moto estmato pre-codg ad etropy codg. ll of these operatos are performed o a block bass. I ths work we use three ecoder complexty cotrol parameters k ( = [ ( k ( k ( k ] where ( k s the umber of SD (sum of absolute dfferece computatos used moto search; ( k s the umber of skpped blocks; ( k s the frame rate. Here k represets the frame umber. he model s traed offle wth trag sequeces. I ths work we use 6 trag vdeo sequeces all QIF (76x44 sze ecoded by MPEG-4 vdeo ecoder at 5 frames per secod. he proposed DGDHP approach for eergy cosumpto cotrol operates at vdeo frame level. he objectve s to mmze the overall vdeo dstorto uder the eergy costrat. We choose two test QIF vdeo sequeces arphoe ad oastgurad show Fg. 6 to evaluate the proposed approach. Each sequece has frames. Fg. 7 shows the average vdeo dstorto (dotted les acheved by the proposed approach o arphoe. It also shows sold les the groud truth optmum obtaed by operatoal P-R-D aalyss. he result for oastguard s show Fg. 8. It ca be see that the performace gap betwee them s very small. hs dcates that the proposed approach for real-tme eergy cosumpto cotrol ad optmzato s very effectve. V. VI. ONUSION Eergy cosumpto cotrol ad optmzato for real-tme vdeo ecodg over portable vdeo commucato devces s a very challegg task sce the ecoder s hghly olear wth very complex eergy cosumpto behavors. Operatoal P-R-D aalyss s too computatoally tesve ad s ot sutable for real-tme applcato. I ths work we have developed a adaptve crtc desg approach for eergy cosumpto cotrol ad optmzato. Our expermetal results demostrate that ths approach s very effcetly beg able to acheve the optmum performace accurately ad robustly. 4

5 Fgure 6: test vdeo clps: arphoe ad oastguard. Fgure 7: Eergy cosumpto cotrol result ad the groudtruth optmum o arphoe vdeo. []. Skora he MPEG-4 vdeo stadard verfcato model IEEE ras. o rcuts ad Systems for Vdeo echology vol. 7 pp. 9 February 997. [] W. P. Burleso P. Ja ad S. Vekatrama Dyamcally Parameterzed rchtecture for Power- ware Vdeo odg: Moto Estmato ad D Proceedgs of the Secod USF Iteratoal Workshop o Dgtal ad omputatoal Vdeo. [4] D. G. Sachs S. dve D.. Joes ross-layer daptve Vdeo odg to Reduce Eergy o Geeral-Purpose Processors Proceedgs of the Iteratoal oferece o Image Processg (IIP Barceloa Spa September. [5] Bellma R.E. Dyamc Programmg Prceto Uversty Press 957. [6] Prokhorov D. & D. Wusch "daptve rtc Desgs" IEEE rasactos o Neural Networks vol. 8 (5 997 pp [7] Prokhorov D. R. Satago & D. Wusch "daptve rtc Desgs: ase Study for Neurocotrol" Neural Networks vol. 8 (9 pp [8] W. P. Burleso P. Ja ad S. Vekatrama Dyamcally Parameterzed rchtecture for Power- ware Vdeo odg: Moto Estmato ad D Proceedgs of the Secod USF Iteratoal Workshop o Dgtal ad omputatoal Vdeo. [9] M. va der Schaar ad Y. dreopoulos Ratedstorto-complexty Modelg for Network ad Recever ware daptato IEEE rasactos o Multmeda vol. 7 o. pp Jue 5. [] Z. He ad S. K. Mtra Ufed Rate-Dstorto alyss Framework for rasform odg IEEE rasactos o rcuts ad System o Vdeo echology vol. pp. -6 December. Fgure 8: Eergy cosumpto cotrol result ad the groudtruth optmum o oastguard vdeo. KNOWEDGEMEN hs work has bee supported part by NSF uder grat DBI-598. REFERENES [] Z. He Y. ag. he I. hmad ad D. Wu Powerrate-dstorto aalyss for wreless vdeo commucato uder eergy costrat IEEE rasactos o rcuts ad System for Vdeo echology May 5. 5